Electric coupling circuits



Se t. 20, 1932. H. A. WHEELER 1,878,653

ELECTRIC COUPLING CIRCUI-TS I Filed Aug. 20,1930

W INVENTOR yarn/a A l l fieeirr [31444.21 ATTORNEYS Patented Sept, 20, 132

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HAROLIWA. WHEELER, OF GREAT NECK, NEW Y0, ASSIGNOR T6 HAZELTINE CORPORATION,-A GORPOfiRATION OF DELAWARE ELECTRIC COUPLING CIRCUITS;

Application filed August 20, 1980. Serial No. 476,542.

This invention relates to high frequency electric coupling circuits tunable over a range in frequency and adapted more especially for interconnecting successive elements of a high g frequency thermionic amplifier or radio system.

The coupling circuits of the present invention are characterized in that the voltage amplification produced thereby is caused to 10 vary automatically with the frequency of tuning in a manner which is under the control of the designer; the designin general being preferably such as to produce a substantially constant resultant amplification, i. e. uniform sensitivity throughout the tunable frequency range.

With an elementary type of 'high frequency coupling circuit of which a closely coupled two-winding transformer having a tunable secondary is a typical example, the

variation in amplification with frequency is not under control of the designer; but increases with frequency throughout the tunable range, in a manner well understood, with consequent detrimental effects including extreme non-uniformity of amplification.

In the elementary type of coupling circuit/ referred to, there exists between the primary and tunablesecondary circuits a degree of coupling which is substantially constant throughout the tunable range, a condition which is partially responsible for the mentioned increase in amplification with frequency. The coupling circuit of the present invention avoids theresulting disadvantages by proper inclusion of suitable reactance elements adapted to provide an efiective coupling between the input and tunable output circuits which automatically decreases with increase in the tuned frequency, and which may be proportioned to offset wholly or in part the factors operative to produce an increase in amplification with frequency.

Coupling circuits broadly operative in ac- 5 cordance with the principles disclosed herein but differing from the present invention as regards both circuit connections and the specific modes of operation thereof, are set forth in Patent No. 1, 763,380 issued to C. E. Trube,

0 and in copending applications Serial No.

101,906, filed April 14, 1926, and Serial No. 120,045, filed July 2, 1926.

The coupling circuits of the present invention embody the following essential elements,

namely: a tunable secondary circuit including q a fixed inductive winding and a variable tuning capacity bridge between a pair of output terminals, and a primary circu1t including in closed series connection in the order recited, a fixed inductance magnetically uncoupled from said secondary winding, a primary winding magnetically coupled to the secondary, a fixed capacity, and a portion of the secondary winding of relatively few turns compared to the fixed inductance. One input terminal is connected at a point between the primary winding and a fixed capacity, and the other input terminal is connected at a point between the secondary winding and said fixed inductance, a terminal of the sec ondary winding being thereby connected directly to one input terminal.

Due to the manner of connecting the input terminals to the primary circuit a pair of parallel paths are provided therebetween, one of which contains the primary. winding and the fixed inductance while the other path contains the fixed capacity and the mentioned portion of the secondary winding. The primary winding and the secondary portion inso cluded in the primary circuit are connected with opposite polarities relative to the input terminals.

An additional capacity may or may not be connected between the input' terminals, or in 85.

the operation of the circuit, capacity may exist between these terminals due to the impedance ofthe input circuit connected thereto.- Irrespective of'the particular arrangement used, the resultant capacity associated with the inductance of the primary circuit, including the fixed capacity of the closed series connection as well as any capacity existing between the input terminals, should be such as to make the primary circuit resonant at a frequency lower but not greatly lower than the lowest frequency within the tunable range.

The objects attained by such design (1) prdvide an eifective coupling'between prition of the circuit connections set forth in the drawing of which:

Fig. 1 shows in diagrammatic form the ele-' mentary coupling circuit of the present invention;

Fig. 2 shows the coupling circuit of Fig.

1 as utilized for connecting an antenna cir- 90 cuit to the input of a thermionic valve; while Fig. 3 is a diagrammatic representation of the circuit of Fig. 1 as employed for interconnecting a pair of thermionic valves in cascade relation.

Figure 4 is a diagrammatic representation of a preferred arrangement of coil elements L and L for employing the natural capacity between said coils to provide capacity C Like elements are similarly designated in the several figures.

' Referring to the drawing, the coupling circuit comprises a resonant secondary circuit consisting of a fixed inductive winding L and a variable tuning condenser G connected in parallel between output terminals 0; and a primary circuit associated with input terminals I which includes in closed series connection in the order recited, a fixed inductance L a primary winding L magnetically coupled to the secondary, a fixed capacity C, and a portion L of the secondary winding L, of relatively few turns compared to L The input terminals I are connected respectively betweenthe primary winding L and fixed capacity C and between the fixed inductance L and the portion L of the secondary winding in such manner that the lower input terminal is connected to a terminal of the secondary winding.

The capacity 0 shown dotted, is intended to represent the entire capacity connected between the input terminals while the circuit is in operation. The largest inductance in the primary circuit is L. This inductance combined with the other elements associated therewith, is resonant at a frequency lower but not greatly lower than the lowest frequency within the tunable range determined by the adjustment of the tuning condenser C.

It is not essential to'the operation of the circuit that a capacity C exist between the input terminals I. In the event that the capacity G is zero, however, it is required that the 85 capacity 0 be of such magnitude as to make the primary circuit resonant at the low frequency above specified.

The elements of the primary circuit as thus proportionedassure that the path between the input terminals containing the elements G and L will be capacitively reactive and hence of decreasing impedance for increases 1n tuning frequency; whereas the path containing elements L and L being inductively reactive, increases in reactance with the frequency of tuning. Thus it will be apparent that the windings L and L produce efi'ects in the secondary circuit which vary in opposite fashion with the tuning: adjustment. The circuit including winding L has its greatest effect at the higher tuned frequenc1es due to approach, to series resonance between condenser 0 and the relatively small effective inductance of winding L The oilcuit including winding L is most effective at the lower tuned frequencies as the result of approach to parallel resonance at the mentioned frequency below the tuning range of the primary circuit as a whole, i. e., windings L and L and the total capacity effectively in shunt thereto.

By properly proportioning these effects which vary oppositely with frequency and combining them in the secondary circuit in additive relation, a resulting effective coupling is attained between primary and tuned secondary circuits which may be caused automatically to decrease with increase in tuned frequency, in a manner which is under control of the designer, and which with sufiicient accuracy is expressed by the following equation:

where 7 is the frequency-of tuning, f is the respnance frequency of the primary circuit, an

M, and M are the mutual inductances between windings L and L and between L and L respectively, while the symbols C and 0 have the significance indicated in the drawmg.

The additive effects of windings L and L upon the tunedgcircuit LG are obtained by connecting these windings in opposite open circuit polarity between the input terminals I. This reversal of connection is required to offset the substantial phase opposition of the primary circuit currents flowing in the paths O L and L L respectively, resulting from the predominant capacitive reactance of the former and the inductive reactance of the latter throughout the tunable frequency range.

In Fig. 2 the input terminals I of the coupling circuit are connected to an antenna 1 and ground 2 respectively, while the output terminals 0 are connected respectively to grid and cathode of a thermionic tube V. The capacity C of Fig. 1 comprises in Fig. 2 the effective antenna-to-ground capacity which in conjunction with capacity C makes the primary circuit resonant at the mentioned fre quency below the tunable ran e.

In Fig. 3 the coupling circuit of Fig. 1 interconnects a pair of thermionic tubes V and V in cascade relation. The input terminals I are connected to anode and cathode of tube V while the output terminals 0 are joined pt; grid and cathode respectively of the tube 2'. The space current for tube V is-supplied from a battery B serially included in the shunt path containing elements L and L with the negative battery terminal connected to the grounded conductor 3.

The capacity C of Fig. lcomprises in Fig. 3 the anode-to-ground capacity of tube V which, in conjunction with the capacity C should be such as to tune the inductance of the primary circuit to the low frequency above specified.

. Reverting again to Fig. 1, the capacityfl may be a physical condenser connected between windings L and L, or winding L may be placed in close proximity to winding L, as by winding the former about the latter, so that the natural capacity between windings will provide the necessary capacity C for completing the primary circuit. In such event the lower terminal of winding L would belconnected only to the upper input termina A preferred arrangement of coils L and L, tov secure natural capacity as C is as follows. A layer of insulatin material is placed over the winding L, and 3 is wound thereon with the same direction and pitch of winding as used in L. The lower end of L is just over the part of L where the tap would otherwise be connected, and the upper end of L is toward the upper end of L. This structure is equallyapplicable to Figs. 1, 2 and 3. y

. Fig. 4 shows the physical arrangement of coil elements for employing the natural ca pacity between coils L and L to provide the capacity 0 Coil L,'as shown, is wound in a single layer upon any suitable formcf insulating material. oil L is in turn wound in a single layer upon and in the same sense with coil L. Coil L which is form wound is situated adjacent the high potential end of coil L with its axis intersecting the axis of coil L at right angles. This arrangement minimizes the magnetic coupling between coil L and coil L.

The upper input terminal I is connectedto the high potential termin'alof coil L the low potential terminal of which is connected terminals 0 in (parallel with the variable tuning condenser t will be noted that in Figs. 2 "and 3 the rotor element of the tuning condenser C is adapted to be grounded directly, constituting a very desirable feature, in that it eliminates certain accidental undesired couplings between difierent parts of the entire circuit.

What is claimed is:

1. An electric coupling system'comprising a tunable secondary circuit including a fixed secondary winding and a variable capacity bridged between output terminals; and a primary circuit including in closed series connection in the order recited, a fixed inductance, a primary winding magnetically coupled to said secondary, a fixed capacity and a portion of said secondary winding, input terminals connected between said primary winding and said fixed capacity and between said fixed inductance and said sec ondary winding respectively, said fixed in-v ductance together with associated capacity being resonant at a frequency slightly below the tunable range, for controlling throughout said frequency range the resultant coupling between said primary and secondaryv ioo consisting of a fixed secondary winding andv terminals; and a primary circuit including in-closed series connection in the order recited, a fixed inductance, a primary winding magnetically coupled to said secondary, a fixed capacity and a portion of said secondary winding of relatively few turns compared to the said fixed inductance, input terminals connected between the said primary winding and fixed capacity and between said fixed inductance and secondary winding terminal respectively, said primary winding and secondary winding portion being connected with opposite polarities relative to said input terminals, and said fixed inductance together with associated capacities including any capacity effectively bridged between said input terminals in the operation of said circuit,-being resonant at a frequency variable capacity bridged between output slightly below the tunable range, for conpacity bridged between grid and cathode of V a therminonic valve, and a prlmary circuit including in closed series connection in the 7 order recited, a fixed inductance, a prima windin magnetically coupled to the secon ary, a xed capacity, and a portion of said secondary winding of relatively few turns compared. to said fixed inductance, input terminals connected between said primary winding and fixed capacity and between said fixed inductance and secondary winding respectively, and an antenna circuit connected to said input terminals, the inductance of 7 said primary circuit together with the associated capacities including the capacity of said antenna circuit, being resonant at a frequency below the tunable range.

4. In a high frequency thermionic amplifier, the combination of an electric coupling circuit comprising a tunable secondary circuit including a fixed secondary winding and variable capacity bridged between grid and cathode of a first thermionic tube, and a primary circuit including in closed series connection in the order recited, a fixed inductance, a primary winding magnetically coupled to said secondary, a fixed capacity, and a terminal portion of said secondary winding, of relatively few turns compared to said fixed inductance, a second thermionic tube having an anode connected between said primary winding and fixed capacity and a cathode connected between said fixed inductance and secondary winding terminal, and said fixed inductance together with the associate capacities including the anode-toground capacity of said second thermionic tube, being resonant'at a frequency slightly lowerthan the lowest frequency within the tunable range, for providing throughout said frequency range uniformly high amplification in the operation of said system.

In testimony whereof I aflix my signature.

HAROLD A. WHEELER 

